Feed unit and feed system

ABSTRACT

A feed unit includes: a power transmission section configured to perform power transmission with use of a magnetic field or an electronic field; a power limiting section provided on a power supply line from an external power source to the power transmission section; and an operation stop section configured to forcibly stop the power transmission. The operation stop section forcibly stops the power transmission when a voltage between an input and an output of the power limiting section exceeds a first threshold. The power limiting section forcibly interrupts power supply to the power transmission section when the voltage between the input and the output exceeds a second threshold that is larger than the first threshold.

TECHNICAL FIELD

The present disclosure relates to a feed system performing non-contactpower supply (power transmission) on a unit to be fed with power such asan electronic apparatus, and to a feed unit applied to such a feedsystem.

BACKGROUND ART

In recent years, a feed system (a non-contact feed system, or a wirelesscharging system) performing non-contact power supply (powertransmission) on consumer electronics devices (CE devices) such asmobile phones and portable music players has attracted attention.Accordingly, charging is allowed to be started by not inserting(connecting) a connector of a power supply such as an AC adapter into aunit but placing an electronic apparatus (a secondary-side unit) on acharging tray (a primary-side unit). In other words, terminal connectionbetween the electronic apparatus and the charging tray is unnecessary.

As a method of performing non-contact power supply in such a way, anelectromagnetic induction method is well known. In addition, anon-contact feed system using a method called magnetic resonance methodthat uses electromagnetic resonance phenomenon has attracted attention.Such a non-contact feed system has been disclosed in, for example, PTLs1 to 6.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.    2001-102974-   PTL b 2: International Publication No. WO00-27531-   PTL 3: Japanese Unexamined Patent Application Publication No.    2008-206233-   PTL 4: Japanese Unexamined Patent Application Publication No.    2002-34169-   PTL 5: Japanese Unexamined Patent Application Publication No.    2005-110399-   PTL 6: Japanese Unexamined Patent Application Publication No.    2010-63245

SUMMARY OF INVENTION

Incidentally, in the non-contact feed system described above, a powertransmission section in a feed unit may be in a failed state or adestructed state (destructive state) in some cases. However, even in thecase of such a failed state or such a destructive state, avoidance ofpossibility of heat generation in the feed unit or the like andsecurement of safety are desired. Therefore, proportion of a method thatallows improvement in safety in power transmission (non-contact powerfeeding) using a magnetic field or the like, is desired.

It is desirable to provide a feed unit and a feed system that arecapable of improving safety in power transmission using a magnetic fieldor an electric field.

According to an embodiment of the present disclosure, there is provideda feed unit including: a power transmission section configured toperform power transmission with use of a magnetic field or an electricfield; a power limiting section provided on a power supply line from anexternal power source to the power transmission section; and anoperation stop section configured to forcibly stop the powertransmission. The operation stop section forcibly stops the powertransmission when a voltage between an input and an output of the powerlimiting section exceeds a first threshold. The power limiting sectionforcibly interrupts power supply to the power transmission section whenthe voltage between the input and the output exceeds a second thresholdthat is larger than the first threshold.

According to an embodiment of the present disclosure, there is provideda feed system provided with one or a plurality of electronic apparatuses(units to be fed with power) and a feed unit configured to perform powertransmission on the electronic apparatuses. The feed unit includes: apower transmission section configured to perform the power transmissionwith use of a magnetic field or an electronic field; a power limitingsection provided on a power supply line from an external power source tothe power transmission section; and an operation stop section configuredto forcibly stop the power transmission. The operation stop sectionforcibly stops the power transmission when a voltage between an inputand an output of the power limiting section exceeds a first threshold,and the power limiting section forcibly interrupts power supply to thepower transmission section when the voltage between the input and theoutput exceeds a second threshold that is larger than the firstthreshold.

In the feed unit and the feed system according to the respectiveembodiments of the present disclosure, the power transmission isforcibly stopped when the voltage between the input and the output ofthe power limiting section exceeds the first threshold. In addition, thepower supply to the power transmission section is forcibly interruptedwhen the voltage between the input and the output exceeds the secondthreshold that is larger than the first threshold. Therefore, forexample, even when the power transmission section is in a failed stateor in a destructive state (even when the operation stop section is in aninoperable state or the like), possibility of heat generation in thefeed unit is avoided.

In the feed unit and the feed system according to the respectiveembodiments of the present disclosure, the operation stop sectionforcibly stops the power transmission when the voltage between the inputand the output of the power limiting section exceeds the firstthreshold, and the power limiting section forcibly interrupts the powersupply to the power transmission section when the voltage between theinput and the output exceeds the second threshold that is larger thanthe first threshold. Therefore, for example, even when the powertransmission section is in the failed state or in the destructive state,possibility of heat generation in the feed unit is allowed to beavoided. Consequently, it is possible to improve safety in the powertransmission using a magnetic field or an electric field.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an appearance configurationexample of a feed system according to a first embodiment of the presentdisclosure.

FIG. 2 is a block diagram illustrating a detailed configuration exampleof the feed system illustrated in FIG. 1.

FIG. 3 is a circuit diagram illustrating a detailed configurationexample of each block illustrated in FIG. 2.

FIG. 4 is a timing waveform chart illustrating an example of a controlsignal to an AC signal generation circuit.

FIG. 5 is a timing chart illustrating an example of a feeding period anda communication period.

FIG. 6 is a timing waveform chart illustrating an example ofcommunication operation by pulse width modulation with use of the ACsignal generation circuit.

FIG. 7 is a characteristic diagram schematically illustrating an exampleof drooping characteristics in an overload state.

FIG. 8 is a timing waveform chart for explaining power limitingdistribution function in the overload state.

FIG. 9 is a schematic diagram for explaining forcible operation stopfunction and forcible power supply interruption function.

FIG. 10 is a circuit diagram illustrating a configuration example of amain part in a feed system according to a second embodiment.

FIG. 11 is a timing chart illustrating an operation example of a powerlimiting modulation circuit illustrated in FIG. 10.

FIG. 12 is a timing waveform chart illustrating an example ofcommunication operation by amplitude modulation with use of the powerlimiting modulation circuit illustrated in FIG. 10.

FIG. 13 is a block diagram illustrating a schematic configurationexample of a feed system according to a modification.

FIG. 14 is a schematic diagram illustrating an example of propagationstate of an electric field in the feed system illustrated in FIG. 13.

DESCRIPTION OF EMBODIMENTS

Some embodiments of the present disclosure will be described in detailbelow with reference to drawings. Note that description will be given inthe following order.

-   1. First embodiment (an example of performing communication by pulse    width modulation with use of an AC signal generation circuit)-   2. Second embodiment (an example of also performing communication by    amplitude modulation with use of a power limiting circuit)-   3. Modifications (an example of a feed system performing non-contact    power transmission using an electric field, etc.)

First Embodiment (General Configuration of Feed System 4)

FIG. 1 illustrates an appearance configuration example of a feed system(a feed system 4) according to a first embodiment of the presentdisclosure, and FIG. 2 illustrates a block configuration example of thefeed system 4. The feed system 4 is a system (a non-contact feed system)performing non-contact power transmission (power supply, power feeding,or power transmission) with use of a magnetic field (with use ofmagnetic resonance, electromagnetic induction, and the like, hereinafterthe same). The feed system 4 includes a feed unit 1 (a primary-sideunit), and one or a plurality of electronic apparatuses (in this case,two electronic apparatuses 2A and 2B, secondary-side units) as units tobe fed with power.

As illustrated in FIG. 1, for example, in the feed system 4, theelectronic apparatuses 2A and 2B are placed (or closely disposed) on afeeding surface (a power transmission surface) S1 of the feed unit 1 sothat the power transmission is performed from the feed unit 1 to theelectronic apparatuses 2A and 2B. In this case, in consideration of thecase where the power transmission is performed to the plurality ofelectronic apparatuses 2A and 2B at the same time or in atime-divisional manner (sequentially), the feed unit 1 has a mat shape(a tray shape) in which an area of the feeding surface S1 is larger thanthe size of the electronic apparatuses 2A and 2B, etc., to be fed withpower.

(Feed Unit 1)

As described above, the feed unit 1 is a unit (a charging tray)transmitting power (performing power transmission) to the electronicapparatuses 2A and 2B with use of a magnetic field. As illustrated inFIG. 2, for example, the feed unit 1 may include a power transmissionsection 110, a current detection circuit 111, a power limiting circuit112, a power transmission device 11 including an AC signal generationcircuit (high-frequency power generation circuit) 113 and an operationstop circuit 114, and a data transmission section 13. Moreover, the feedunit 1 may include a control section 10 including a power transmissioncontrol section (a modulation processing section) 10A that is providedin the power transmission device 11 and a data transmission controlsection 10B that is provided outside the power transmission device 11.Among them, the power limiting circuit 112, the AC signal generationcircuit 113, the operation stop circuit 114, and the data transmissioncontrol section 10B correspond to specific examples of “power limitingsection”, “AC signal generation section”, “operation stop section”, and“data transmission control section”, respectively.

The power transmission section 110 is configured to include a powertransmission coil (a primary-side coil) L1, capacitors C1 p and C1 s(resonance capacitors), and the like, that will be described later. Thepower transmission section 110 uses the power transmission coil L1 andthe capacitors C1 p and C1 s to transmit power (perform powertransmission) to the electronic apparatuses 2A and 2B (in detail, apower reception section 210 described later) with use of an AC magneticfield (see an arrow P1 in FIG. 2). More specifically, the powertransmission section 110 has a function of radiating a magnetic field (amagnetic flux) from the feeding surface S1 toward the electronicapparatuses 2A and 2B. The power transmission section 110 further has afunction of performing predetermined mutual communication operation withthe power reception section 210 described later (see an arrow C1 in FIG.2).

For example, the AC signal generation circuit 113 is a circuit that usespower supplied from an external power source 9 (a master power source)of the feed unit 1 through the power limiting circuit 112 describedlater to generate a predetermined AC signal Sac (high-frequency power)to transmit power. Such an AC signal generation circuit 113 may beconfigured using, for example, a switching amplifier described later.Note that, as the external power source 9, for example, a power source(power supply capacity: 500 mA, source voltage: about 5 V) of universalserial bus (USB) 2.0 that is provided in personal computer (PC) or thelike may be used.

The power limiting circuit 112 is provided on a power supply line (apower supply line Lp described later) from the external power source 9to the power transmission section 110, namely, between a power inputterminal (not illustrated) for the external power source 9 and the powertransmission section 110. The power limiting circuit 112 has a functionof limiting (performing power limiting operation) power supplied fromthe external power source 9 to the power transmission section 110. Morespecifically, although the detail will be described later, the powerlimiting circuit 112 functions as an overcurrent limiting circuit (anovercurrent protection circuit) that limits an overcurrent in anoverload state, or the like. In addition, the power limiting circuit 112has a function of forcibly interrupting power supply from the externalpower source 9 to the power transmission section 110 in a predeterminedcase described later.

The current detection circuit 111 is a circuit detecting an inputcurrent I1 that flows from the external power source 9 to the entirefeed unit 1. Specifically, the current detection circuit 111 detects(measures) a voltage corresponding to the input current I1 to output thevoltage to the power limiting circuit 112.

The operation stop circuit 114 is a circuit that forcibly stops powertransmission by the power transmission section 10 and the like,irrespective of the power transmission control by the power transmissioncontrol section 10A described later, when an abnormal state (an overloadstate or the like) of the unit described later is detected.

The data transmission section 13 performs non-contact mutual datatransmission with a data transmission section 23 described later in theelectronic apparatuses 2A and 2B (see an arrow D1 in FIG. 2).Incidentally, examples of a method of performing such non-contact datatransmission may include a method using “Transfer Jet” that is one ofshort distance wireless transfer technologies.

As illustrated in FIG. 2, the control section 10 is provided in apreceding stage of the power limiting circuit 112 (on a side closer tothe external power source 9 than the power limiting circuit 112),namely, between the power input terminal (not illustrated) for theexternal power source 9 and the power limiting circuit 112. The controlsection 10 is configured to include the power transmission controlsection 10A that controls power transmission by the power transmissionsection 110, and the data transmission control section 10B that controlsdata transfer by the data transmission section 13, and performs variouscontrol operation in the entire feed unit 1 (the entire feed system 4).More specifically, the control section 10 may include a function ofperforming proper control of the transmitted power, a function ofauthenticating a secondary-side unit, a function of determining whethera secondary-side unit is placed on a primary-side unit, a function ofdetecting a contaminant such as dissimilar metal, and the like, inaddition to the above-described function of power transmission controland the data transmission control.

The power transmission control section 10A controls the operation of theAC signal generation circuit 113 (in this case, through the operationstop section 114) with use of a predetermined control signal CTL (acontrol signal for power transmission) described later, to perform theabove-described power transmission control. Moreover, the powertransmission control section 10A has a function of performing modulationprocessing by pulse width modulation (PWM) described later with use ofthe control signal CTL.

(Electronic Apparatuses 2A and 2B)

For example, the electronic apparatuses 2A and 2B are each configured ofa stationary electronic apparatus typified by a television receiver, aportable electronic apparatus including a rechargeable battery(battery), typified by a mobile phone and a digital camera, or the like.For example, as illustrated in FIG. 2, these electronic apparatuses 2Aand 2B each may include a power reception device 21, a load 22 thatperforms predetermined operation (operation exerting functions as anelectronic apparatus) based on power supplied from the power receptiondevice 21, and the data transmission section 23. In addition, the powerreception device 21 may include the power reception section 210, arectification circuit 211, a charging circuit 212, and a battery 213.

The power reception section 210 is configured to include a powerreception coil (a secondary-side coil) L2, capacitors C2 p and C2 s(resonance capacitors), and the like, that will be described later. Thepower reception section 210 has a function of receiving powertransmitted from the power transmission section 110 in the feed unit 1with use of the power reception coil L2, the capacitors C2 p and C2 s,and the like. The power reception section 210 further has a function ofperforming the above-described predetermined mutual communicationoperation with the power transmission section 110 (see the arrow C1 inFIG. 2).

The rectification circuit 211 is a circuit that rectifies the power (ACpower) supplied from the power reception section 210 to generate DCpower.

The charging circuit 212 is a circuit that performs charging on thebattery 213 or a battery (not illustrated) in the load 22, based on theDC power supplied from the rectification circuit 211.

The battery 213 stores therein power in response to the charging by thecharging circuit 212, and may be configured using a rechargeable battery(a secondary battery) such as a lithium ion battery. Note that, in thecase of using only the battery in the load 22, or the like, the battery213 may be not necessarily provided.

As described above, the data transmission section 23 performs thenon-contact mutual data transmission with the data transmission section13 in the feed unit 1 (see the arrow D1 in FIG. 2).

(Detailed Configurations of Feed Unit 1 and Electronic Apparatuses 2Aand 2B)

FIG. 3 is a circuit diagram illustrating a detailed configurationexample of each block in the feed unit 1 and the electronic apparatuses2A and 2B illustrated in FIG. 2.

(Power Transmission Section 110)

The power transmission section 110 includes the power transmission coilL1 to perform power transmission using a magnetic field (to generate amagnetic flux), and the capacitors C1 p and C1 s to form, together withthe power transmission coil L1, an LC resonance circuit. The capacitorC1 s is electrically connected in series to the power transmission coilL1. In other words, an end of the capacitor C1 s and an end of the powertransmission coil L1 are connected to each other. Moreover, the otherend of the capacitor C1 s and the other end of the power transmissioncoil L1 are connected in parallel to the capacitor C1 p, and theconnection end of the power transmission coil L1 and the capacitor C1 pis grounded.

The LC resonance circuit configured of the power transmission coil L1and the capacitors C1 p and C1 s, and an LC resonance circuit describedlater configured of the power reception coil L2 and the capacitors C2 pand C2 s are magnetically coupled with each other. As a result, LCresonance operation by a resonance frequency that is substantially thesame as that of the high-frequency power (the AC signal Sac) describedlater generated by the AC signal generation circuit 113, is performed.

(Current Detection Circuit 111)

The current detection circuit 111 has a resistor R1 and an erroramplifier A1. An end of the resistor R1 is connected to the power inputterminal (not illustrated) for the external power source 9, and theother end of the resistor R1 is connected to a connection point P0. Inother words, the resistor R1 is disposed on the power supply line Lp. Aninput terminal on a positive side (a plus side) of the error amplifierA1 is connected to the end of the resistor R1, an input terminal on anegative side (a minus side) is connected to the other end of theresistor R1, and an output terminal is connected to an input terminal ona positive side of an error amplifier A3 in the power limiting circuit112, described later. In other words, a potential difference (a voltage)between the both ends of the resistor R1 is input to the input terminalon the positive side of the error amplifier A3.

With such a configuration, the current detection circuit 111 detects theabove-described input current I1 flowing through the resistor R1 (thecurrent flowing through the power supply line Lp), and outputs a voltageV1 corresponding to the magnitude of the input current I from the erroramplifier A1 to the error amplifier A3.

(Power Limiting Circuit 112)

The power limiting circuit 112 includes transistors Tr1 and Tr2, acomparator A2, the error amplifier A3, and the power sources PS2 andPS3. Among them, the transistor Tr1 is configured of a p-type fieldeffective transistor (FET), and the transistor Tr2 is configured of ann-type FET. Moreover, the power source PS2 is a power source outputtinga predetermined threshold voltage Vth2 (>0 V) (a second threshold)described later, and the power source PS3 is a power source outputting areference voltage Vref described later. Note that the transistor Tr1 andthe error amplifier A3 correspond to specific examples of “transistor”and “error amplifier” in the present disclosure, respectively.

A source of the transistor Tr1 is connected to the connection point P0,a drain is connected to an end of each of the above-described capacitorsC1 p and Cs1, and a gate is connected to an output terminal of the erroramplifier A3. In other words, the transistor Tr1 is disposed on thepower supply line Lp. An input terminal on a negative side of thecomparator A2 is connected to an output terminal of a comparator A4described later in the operation stop circuit 114, an input terminal ona positive side is connected to the power source PS2, and an outputterminal is connected to a gate of the transistor Tr2. A source of thetransistor Tr2 is grounded, and a drain is connected to the power sourcePS3 and an input terminal on a negative side of the error amplifier A3.

With this configuration, in the power limiting circuit 112, an outputsignal S3 is generated according to a potential difference between theabove-described output voltage from the error amplifier A1 (the voltageV1 corresponding to the input current ID and the reference voltage Vref,and is supplied to the gate of the transistor Tr1. Then, according tothe output signal S3, magnitude (magnitude of the power) of a current I2(a current flowing through a path from the connection point P0 to thepower transmission section 110 side, out of the above-described inputcurrent I1) flowing between the source and the drain of the transistorTr1 is limited. In this way, the power supplied from the external powersource 9 to the power transmission section 110 is limited (theovercurrent in the overload state or the like is limited).

In addition, in a predetermined case described later, the magnitude ofthe reference voltage Vref input to the error amplifier A3 describedabove is controlled by the operation stop circuit 114, and thus powersupply from the external power source 9 to the power transmissionsection 110 is forcibly interrupted by the power limiting circuit 112.More specifically, according to a comparison result of the voltages inthe comparator A2 described above, the magnitude of the referencevoltage Vref is controlled.

(Control Section 10)

The control section 10 has the power transmission control section (themodulation processing section) 10A and the data transmission controlsection 10B that are described above, and an input terminal of each ofthe sections is connected to the connection point P0. In other words,the power transmission control section 10A and the data transmissioncontrol section 10B are disposed so as to be connected in parallel toeach other in the preceding stage of the power limiting circuit 112(between the external power source 9 and the power limiting circuit112). Therefore, although the detail will be described later, a currentI3 of the above-described input current I1 constantly flows through thepath from the connection point P0 to the control section 10 side(irrespective of the load state).

(Operation Stop Circuit 114)

The operation stop circuit 114 has the comparator A4, a power source PS1outputting a predetermined threshold voltage Vth1 (>Vth2) (firstthreshold) described later, and an AND circuit LG1. Among them, thecomparator A4 and the AND circuit LG1 correspond to specific examples of“voltage detection section” and “switching section” in the presentdisclosure, respectively.

An input terminal on a positive side of the comparator A4 is connectedto the source of the transistor Tr1, and an input terminal on a negativeside is connected to the drain of the transistor Tr1 through the powersource PS1. An output terminal of the comparator A4 is connected to theinput terminal on the negative side of the comparator A2 described aboveand one of input terminals of the AND circuit LG1. In addition, theother input terminal of the AND circuit LG1 is supplied with the controlsignal CTL for power transmission from the power transmission controlsection 10A.

As illustrated in FIG. 3, the control signal CTL is formed of a pulsesignal having a predetermined duty ratio. In addition, for example, asillustrated in (A) and (B) of FIG. 4, controlling the duty ratio of thecontrol signal CTL causes pulse width modulation described later.

With such a configuration, in the operation stop circuit 114, a voltageΔV2 between the input and the output of the power limiting circuit 112(the potential difference between the source and the drain of thetransistor Tr1) is detected by the comparator A4, and is compared withthe above-described threshold voltage Vth1. Then, an abnormal state(such as an overload state) described later of the unit is detectedaccording to the comparison result of the voltages (the magnitude of thedetected voltage ΔV2), and the power transmission operation by the ACsignal generation circuit 113 and the power transmission section 110 isforcibly stopped through the AND circuit LG1, according to the detectionresult.

(AC Signal Generation Circuit 113)

The AC signal generation circuit 113 is configured using a switchingamplifier (a so-called class-E amplifier) that has one transistor Tr3 asa switching device. Moreover, in this example, the transistor Tr3 isconfigured of an n-type FET. A source of the transistor Tr3 is grounded,a gate is connected to the output terminal of the AND circuit LG1described above, and a drain is connected to the drain of the transistorTr1 and the end of each of the capacitors C1 p and C1 s that aredescribed above.

With such a configuration, in the AC signal generation circuit 113, thetransistor Tr3 performs ON-OFF operation (switching operation by apredetermined frequency and the duty ratio), according to the outputsignal (a signal S1) from the AND circuit LG1 based on theabove-described control signal CTL for the power transmission.Specifically, the ON-OFF operation of the transistor Tr3 as theswitching device is controlled with use of the control signal CTLsupplied from the power transmission control section 10A. Accordingly,the AC signal Sac (AC power) is generated based on a DC signal Sdc thatis input through the power limiting circuit 112, and the AC signal Sacis supplied to the power transmission section 110.

(Power Reception Section 210)

The power reception section 210 includes a power reception coil L2 toreceive the power (from the magnetic flux) transmitted from the powertransmission section 110 and the capacitors C2 p and C2 s to form,together with the power reception coil L2, an LC resonance circuit. Thecapacitor C2 p is electrically connected in parallel to the powerreception coil L2, and the capacitor C2 s is electrically connected inseries to the power reception coil L2. In other words, an end of thecapacitor C2 s is connected to an end of the capacitor C2 p and an endof the power reception coil L2. In addition, the other end of thecapacitor C2 s is connected to one of the input terminals of therectification circuit 211, and the other end of the power reception coilL2 and the other end of the capacitor C2 p are connected to the otherinput terminal of the rectification circuit 211.

The LC resonance circuit configured of the power reception coil L2 andthe capacitors C2 p and Cs2 and the above-described LC resonance circuitconfigured of the power transmission coil L1 and the capacitors C1 p andC1 s are magnetically coupled with each other. As a result, LC resonanceoperation by a resonance frequency that is substantially the same asthat of the high-frequency power (the AC signal Sac) generated by the ACsignal generation circuit 113, is performed.

(Function and Effects of Feed System 4)

(1. Outline of General Operation)

In the feed system 4, the AC signal generation circuit 113 in the feedunit 1 supplies predetermined high-frequency power (the AC signal Sac)for power transmission, to the power transmission coil L1 and thecapacitors C1 p and C1 s (the LC resonance circuit) in the powertransmission section 110, based on the power supplied from the externalpower source 9. Accordingly, a magnetic field (a magnetic flux) isgenerated in the power transmission coil L1 in the power transmissionsection 110. At this time, when the electronic apparatuses 2A and 2Bthat are units to be fed with power (to be charged) are placed (orclosely disposed) on a top surface (the feeding surface S1) of the feedunit 1, the power transmission coil L1 in the feed unit 1 and the powerreception coil L2 in each of the electronic apparatuses 2A and 2B arebrought close to each other near the feeding surface S1.

In this way, when the power reception coil L2 is disposed near the powertransmission coil L1 generating the magnetic field (the magnetic flux),electromotive force is generated in the power reception coil L2 byinduction of the magnetic flux generated from the power transmissioncoil L1. In other words, interlinkage magnetic field is generated ineach of the power transmission coil L1 and the power reception coil L2by electromagnetic induction or magnetic resonance. As a result, poweris transmitted from the power transmission coil L1 side (a primary side,the feed unit 1 side, the power transmission section 110 side) to thepower reception coil L2 side (a secondary side, the electronicapparatuses 2A and 2B side, the power reception section 210 side) (seethe arrow P1 in FIG. 2 and FIG. 3). At this time, the power transmissioncoil L1 on the feed unit 1 side and the power reception coil L2 on theelectronic apparatuses 2A and 2B side are magnetically coupled with eachother by the electromagnetic induction or the like, and thus the LCresonance operation is performed in the above-described LC resonancecircuit.

Then, in the electronic apparatuses 2A and 2B, the AC power received bythe power reception coil L2 is supplied to the rectification circuit 211and the charging circuit 212, thereby leading to the following chargingoperation. Specifically, after the AC power is converted intopredetermined DC power by the rectification circuit 211, charging to thebattery 213 or the battery (not illustrated) in the load 22 based on theDC power is performed by the charging circuit 212. In this way, in theelectronic apparatuses 2A and 2B, the charging operation based on thepower received by the power reception section 210 is performed.

In other words, in the present embodiment, terminal connection to an ACadopter or the like is not necessary for charging of the electronicapparatuses 2A and 2B, and charging is easily started (non-contactfeeding is performed) only by placing (closely disposing) the electronicapparatuses 2A and 2B on the feeding surface S1 of the feed unit 1. Thisleads to liability relief of a user.

In addition, for example, as illustrated in FIG. 5, in such feedingoperation, a feeding period Tp (a charging period) and a communicationperiod Tc (a non-charging period) are periodically (or non-periodically)performed in a time-divisional manner. In other words, the powertransmission control section 10A performs control so that the feedingperiod Tp and the communication period Tc are periodically (ornon-periodically) set in a time-divisional manner. In this case, thecommunication period Tc is a period during which mutual communicationoperation (communication operation for mutual authentication betweenunits, feed efficiency control, or the like) is performed between theprimary-side unit (the feed unit 1) and the secondary-side unit (theelectronic apparatuses 2A and 2B) with use of the power transmissioncoil L1 and the power reception coil L2 (see the arrow C1 in FIG. 2 andFIG. 3). Incidentally, the time ratio of the feeding period Tp and thecommunication period Tc at this time may be, for example, the feedingperiod Tp: the communication period Tc=about 9:1.

At this time, for example, as illustrated in (A) to (D) of FIG. 6,during the communication period Tc, the communication operation usingpulse width modulation is performed by the AC signal generation circuit113. Specifically, the duty ratio of the control signal CTL during thecommunication period TC is set (see (B) of FIG. 6), for example, basedon modulation data Dm illustrated in (A) of FIG. 6, and thus thecommunication by the pulse width modulation is performed. Note that,since it is difficult to perform frequency modulation at the time ofresonance operation by the power transmission section 110 and the powerreception section 210 described above, such pulse width modulation isused to achieve the communication operation easily.

Further, in the feed system 4, as illustrated by the arrow D1 in FIG. 2and FIG. 3, non-contact mutual data transmission is performed betweenthe data transmission section 13 in the primary-side unit (the feed unit1) and the data transmission section 23 in the secondary-side unit (theelectronic apparatuses 2A and 2B). Accordingly, the data transmission isallowed to be performed only by bring the electronic apparatuses 2A and2B close to the feed unit 1 without connection of wirings for the datatransmission or the like between the feed unit 1 and the electronicapparatuses 2A and 2B. Thus, this also leads to liability relief of auser.

(2. Power Limiting Distribution Function in Overload State)

Incidentally, in such a feed system 4, load may become excessive(overload state) in some cases in the feed unit 1. Specifically, forexample, a case where the data transmission section 13 consumesexcessive power suddenly, a case where the secondary-side unit (in thiscase, the electronic apparatuses 2A and 2B) demands excessive power, orthe like are assumed.

In such an overload state, for example, as illustrated in FIG. 7,control is performed so that drooping characteristics (fold backcharacteristics) are exhibited in current-voltage characteristics, andprotection against the overcurrent is performed. Specifically, in thiscase, first, the voltage V1 corresponding to the input current I1 fromthe external power source 9 is detected by the current detection circuit111 in the feed unit 1. Then, in the power limiting circuit 112, thesignal S3 according to the potential difference between the voltage V1and the reference voltage Vref is output from the error amplifier A3,and the magnitude of the current I2 flowing between the source and thedrain of the transistor Tr1 is controlled based on the signal S3. Inother words, the magnitude of the current I2 is limited (the powersupplied to the drain side of the transistor Tr1 is limited) accordingto the magnitude of the input current I1, which causes power limitingoperation by the power limiting circuit 112. For example, in the casewhere the external power source 9 is the above-described power source ofUSB 2.0, when I1≧500 mA is established (when the power exceeds 2.5 W),it is determined as overcurrent state (the overload state).

However, if such power limiting operation is applied to the entire feedunit 1 (if power supply is limited with respect to the entire block inthe feed unit 1), the following disadvantage may occur. Specifically,when the above-described overcurrent state (overload state) isestablished, if the power supplied to the control section 10 (inparticular, the power transmission control section 10A) that performscontrol of the entire feed unit 1 (the entire feed system 4) is alsolimited, the operation of the control section 10 is stopped, whichcauses inconvenience. In other words, for example, since the powertransmission control section 10A plays an important role of securingsafety and the like in the feed system 4, even in the overload state orthe like, the power transmission control section 10A is expected toperform normal operation (it is necessary for the power transmissioncontrol section 10A to secure stable operation constantly).

Accordingly, in the feed unit 1 in the present embodiment, asillustrated in FIG. 2 and FIG. 3, the control section 10 is provided inthe preceding stage of the power limiting circuit 112 (between theexternal power source 9 and the power limiting circuit 112). Thus, thecurrent I3 of the input current I1 that flows from the external powersource 9 to the feed unit 1 constantly flows through the path from theconnection point P0 to the control section 10 side (irrespective of theload state) (see FIG. 3). In other words, for example, even in the caseof the overload state or the like, the power supplied from the externalpower source 9 to the control section 10 side is not limited. In thisway, the power supplied to the control section 10 side is constantlyensured in the feed unit 1, and preferential power distribution to thecontrol section 10 side is performed.

Specifically, for example, as illustrated by arrows in (C) of FIG. 8,even when the current I3 consumed by the control section 10 isdrastically increased (even when the overload state is established), thecurrent I3 flowing to the control section 10 side (power supply to thecontrol section 10 side) is not limited. On the other hand, for exampleas illustrated by arrows in (B) of FIG. 8, when such an overload stateis established, the current I2 supplied to the power transmissionsection 110 side that is located in the subsequent stage of the powerlimiting circuit 112 (the power supply to the power transmission section110) is limited by the power limiting circuit 112. In this way, thepower is distributed preferentially to the control section 10 siderather than the power transmission section 110 side.

In addition, at this time, for example, as illustrated by arrows in (A)of FIG. 8, the input current I1 flowing from the external power source 9to the entire feed unit 1 (the power extracted from the external powersource 9) is controlled to be equal to or lower than a predeterminedthreshold Ith (for example, in the case of the above-described powersource of USB 2.0, 500 mA). As a result, supply of excessive power(exceeding supply capacity) (the input current I1 equal to or largerthan the threshold Ith) from the external power source 9 is avoided.Therefore, for example, in the case where the power source of USB 2.0provided in a PC is used as the external power source 9, “Warning” orthe like is prevented from being displayed on a display screen of the PCwhen power exceeding supply capacity of the external power source 9 isintended to be extracted by the feed unit 1.

(3. Forcible Operation Stop Function)

Moreover, in the feed unit 1 in the present embodiment, in the operationstop circuit 114, the following forcible operation stop function isperformed.

Specifically, first, in the comparator A4, the voltage ΔV2 between theinput and the output of the power limiting circuit 112 (the potentialdifference between the source and the drain of the transistor Tr1) isdetected, and magnitude comparison between the voltage ΔV2 and thepredetermined threshold voltage Vth1 is performed. For example, asillustrated in FIG. 9, the threshold voltage Vth1 is a thresholddefining whether the state is the overload state (the overcurrent state)during the normal operation in the feed unit 1. In other words,according to the above-described comparison result of the voltages (themagnitude of the detected voltage ΔV2), whether the state is a properload state or the overload state during the normal operation isdetected. In this case, when the magnitude of the voltage ΔV2 is equalto or lower than the threshold Vth1, it is detected that the state isthe proper load state during the normal operation, and when themagnitude of the voltage ΔV2 exceeds the threshold Vth1, it is detectedthat the state is the overload state during the normal operation.Incidentally, detection sensitivity at this time is set by a timeconstant of a wiring between the comparator A4 and the AND circuit LG1,so as to be slightly dulled.

Then, in the operation stop circuit 114, according to theabove-described detection result of the load state, the powertransmission operation by the AC signal generation circuit 113 and thepower transmission section 110 is forcibly stopped with use of the ANDcircuit LG1, irrespective of the power transmission control by the powertransmission control section 10A. More specifically, when it is detectedthat the state is the proper load state during the normal operation (ΔV2Vth1), the output signal S4 from the comparator A4 becomes “H (high)”state. As a result, the output signal S1 from the AND circuit LG1 to thetransistor Tr3 in the AC signal generation circuit 113 becomes equal tothe control signal CTL for the power transmission supplied from thepower transmission control section 10A (control is performed so that thecontrol signal CTL becomes valid). Therefore, the transistor Tr3performs ON-OFF operation with use of the control signal CTL, and thusthe normal power transmission operation is performed by the AC signalgeneration circuit 113 and the power transmission section 110.

On the other hand, when it is detected that the state is the overloadstate during the normal operation (ΔV2>Vth1), the output signal S4 fromthe comparator A4 becomes “L (low)” state. As a result, the outputsignal S1 from the AND circuit LG1 to the transistor Tr3 in the ACsignal generation circuit 113 is constantly in the “L” state (control isperformed so that the control signal CTL becomes invalid), and thetransistor Tr3 is constantly in the OFF state (the transistor Tr3 is inthe open state). In other words, the AND circuit LG1 plays a role ofswitching the state of the control signal CTL between valid and invalid,according to the value of the output signal S4 from the comparator A4(presence or absence of detection of the overload state). Further, inthe operation stop circuit 114, rendering the control signal CTL for thepower transmission invalid forcibly stops the power transmissionoperation by the AC signal generation circuit 113 and the powertransmission section 110, irrespective of the power transmission controlby the power transmission control section 10A.

In addition, in the operation stop circuit 114, when the above-describedoverload state (the overcurrent state) is detected also during theabove-described communication period Tc in addition to such a feedingperiod Tp, the control signal CTL is similarly rendered invalid toforcibly stop the communication operation.

Note that, when the comparator A4 detects recovery from the overloadstate to the proper load state, the control signal CTL becomes validagain by the above-described principle. Therefore, also in this case,the power transmission operation is automatically restarted irrespectiveof the power transmission control by the power transmission controlsection 10A.

In such a way, when the abnormal state (the overload state) of the feedunit 1 is detected, the power transmission by the power transmissionsection 110 is forcibly stopped irrespective of the power transmissioncontrol by the power transmission control section 10A. Therefore, forexample, when the load state is changed to the overload state or thelike, the power transmission is rapidly stopped without waiting thepower transmission control by the power transmission control section10A, which reduces a time necessary for stopping the power transmission(namely, unnecessary power transmission period).

(4. Forcible Power Supply Interruption Function)

Moreover, the comparator A4 detects that the magnitude of the voltageΔV2 also exceeds the predetermined threshold Vth2 (>Vth1), forciblepower supply interruption function described below is performed in thecurrent limiting circuit 112, irrespective of the power transmissioncontrol by the power transmission control section 10A.

In this case, for example, as illustrated in FIG. 9, the thresholdvoltage Vth2 is a threshold that defines whether the power transmissionsection 110 is in a failed state or a destructed state (destructivestate) due to a short circuit state or the like in the feed unit 1. Insuch a state, the voltage ΔV2 between the both ends of the transistorTr1 in the current limiting circuit 112 may become excessive to generateheat, and the operation stop circuit 114 may become in an inoperablestate (the above-described forcible operation stop function may not beexerted).

As described above, the comparator A4 also detects whether the powertransmission section 110 is in the failed state or the destructive statedescribed above according to the detected magnitude of the voltage ΔV2.Specifically, in this example, when the magnitude of the voltage ΔV2 isequal to or lower than the threshold Vth2, it is detected that the powertransmission section 110 is neither in the failed state nor in thedestructive state. On the other hand, when the magnitude of the voltageΔV2 exceeds the threshold Vth2, it is detected that the powertransmission section 110 is in the failed state or in the destructivestate.

Further, when it is detected that the magnitude of the voltage ΔV2 alsoexceeds the threshold Vth2 (in the failed state or in the destructivestate), the power supply from the external power source 9 to the ACsignal generation circuit 113 and the power transmission section 110side is forcibly interrupted in the current limiting circuit 112 in thefollowing way. In other words, the magnitude of the reference voltageVref input to the error amplifier A3 is controlled according to thecomparison result of the voltages by the comparator A2, the transistorTr1 is constantly in the OFF state, and thus forcibly power supplyinterruption is performed.

More specifically, at this time (ΔV2>Vth2), the output signal S2 fromthe comparator A2 becomes “L” state, and thus the transistor Tr2 is putinto OFF state. Therefore, the potential of the input terminal on thenegative side of the error amplifier A3 is drawn from the originalreference voltage Vref supplied from the power source PS3 to the ground(0 V) side, and is lowered. As a result, the output signal S3 from theerror amplifier A3 becomes “H” state, and the transistor Tr1 isconstantly in OFF state. In this way, when the transistor Tr1 is putinto OFF state, the current I2 does not flow between the source and thedrain (I2=0 A), and the power supply to the power transmission section10 side is forcibly interrupted. Further, even when the stop function ofthe current I2 by such a positive feedback (overcurrent suppressingfunction) is acted and the operation stop circuit 114 becomes aninoperable state, the power limiting circuit 112 operates until theovercurrent completely stops and thus possibility of heat generation inthe transistor Tr1 described above is avoided. In other words, even whenthe power transmission section 110 is in the failed state or in thedestructive state (even when the operation stop circuit 114 is in theinoperable state or the like), possibility of the heat generation in thefeed unit 1 is avoided.

As described above, in the present embodiment, the operation stopcircuit 114 forcibly stops the power transmission when the detectedvoltage (the voltage ΔV2) exceeds the threshold voltage Vth1, and thepower limiting circuit 112 forcibly interrupts the power supply to thepower transmission section 110 when the voltage ΔV2 exceeds thethreshold voltage Vth2 that is larger than the threshold voltage Vth1.Therefore, for example, even when the power transmission section 110 isin the failed state or in the destructive state, the overcurrent isallowed to be completely stopped, and possibility of the heat generationin the feed unit 1 (the transistor Tr1) is allowed to be avoided.Accordingly, it is possible to improve safety in the power transmissionusing a magnetic field.

Moreover, when the abnormal state (the overload state) of the feed unit1 is detected, the operation stop circuit 114 forcibly stops the powertransmission irrespective of the power transmission control by the powertransmission control section 10A. Therefore, for example, when the loadstate is changed to the overload state or the like, unnecessary powertransmission period is allowed to be reduced. Consequently, in the powertransmission using a magnetic field, it is possible to reduce power losscaused by the change of the load state.

Further, the control section 10 is provided on a side closer to theexternal power source 9 than the power limiting circuit 112. Therefore,the power supply from the external power source 9 to the control section10 side is constantly ensured, which allows preferential powerdistribution to the control section 10 side. Therefore, the stableoperation of the control section 10 is ensured, and proper control isallowed to be achieved irrespective of the load state when the powertransmission is performed with use of a magnetic field. In addition,clarifying the responsibilities of the power source protection and thepower distribution in the feed system 4 (the non-contact feed system)provides an effect of securing safety.

In addition, in the case where the power transmission is performed bythe power transmission section 110 with use of resonance operation (LCresonance operation), the following advantage is particularly obtained.Specifically, since resonance operation is acted, the configuration thatis insensitive to the variation of the output power and has resistanceto instant power interruption or the like is obtained. In other words,even if sudden power variation occurs, the power transmission section110 is allowed to continue to operate (continue to transmit power) by aso-called “principle of pendulum” (inertia action).

Second Embodiment

Subsequently, a second embodiment of the present disclosure will bedescribed. Note that like numerals are used to designate substantiallylike components of the above-described first embodiment, and descriptionthereof will be appropriately omitted.

(Configuration of Feed System 4A)

FIG. 10 is a circuit diagram illustrating a configuration example of amain part in a feed system (a feed system 4A) according to the secondembodiment. The feed system 4A in the present embodiment has one feedunit 1A and two electronic apparatuses 2A and 2B. The feed unit 1A isconfigured by providing a power limiting modulation circuit 112A in thefeed unit 1 of the first embodiment in place of the power limitingcircuit 112, and other configurations are similar to those in the feedunit 1 of the first embodiment. Note that the power limiting modulationcircuit 112A corresponds to a specific example of “power limitingsection” in the present disclosure.

In this example, as illustrated in FIG. 10, the power limitingmodulation circuit 112A has a configuration in which one OR circuit LG2is further added to the power limiting circuit 112 illustrated in FIG.3. One of input terminals of the OR circuit LG2 is connected to theoutput terminal of the error amplifier A3, and the other input terminalreceives the modulation data Dm output from the power transmissioncontrol section (the modulation processing section) 10A. An outputterminal of the OR circuit LG2 is connected to the gate of thetransistor Tr1.

(Function and Effects of Feed System 4A)

In the feed unit 1A of the present embodiment, in the power limitingmodulation circuit 112A, power limiting operation is performed by asimilar method to that by the power limiting circuit 112 of the firstembodiment. In addition thereto, in the power limiting modulationcircuit 112A, amplitude modulation (AM) operation such as amplitudeshift keying (ASK) modulation is performed.

Specifically, for example, as illustrated in FIG. 11, in the powerlimiting modulation circuit 112A, the power limiting operation isperformed during the feeding period Tc, whereas the amplitude modulationoperation is performed during the communication period Tc. Further,during the communication period Tc (in a light load state), the powerlimiting operation of the power limiting modulation circuit 112A iscontrolled by the power transmission control section 10A, and thuscommunication by the above-described amplitude modulation is performed.In this way, in the present embodiment, the communication operation bythe amplitude modulation such as ASK modulation is achieved relativelyeasily.

More specifically, during the communication period Tc, for example, asillustrated in (A) to (D) of FIG. 12, the communication operation usingthe amplitude modulation in the power limiting modulation circuit 112Ais performed. In other words, for example, the modulation data Dmillustrated in (A) of FIG. 12 is first supplied from the powertransmission control section 10A to the transistor Tr1 through the ORcircuit LG2 in the power limiting modulation circuit 112A. As a result,the DC signal Sdc output from the power limiting modulation circuit 112Ato the power supply line Lp is a signal subjected to the amplitudemodulation, for example, as illustrated in (B) of FIG. 12. Then, the ACsignal Sac is generated by the AC signal generation circuit 113 based onsuch a DC signal Sdc (see (C) of FIG. 12), and the communicationoperation by the amplitude modulation is finally performed (see (D) ofFIG. 12).

By the communication operation by the amplitude modulation using thepower limiting operation of the power limiting modulation circuit 112A,for example, the following advantages are obtainable, for example, ascompared with the communication operation using pulse width modulationof the AC signal generation circuit 113 described in the firstembodiment.

Specifically, for example, as illustrated by a dashed line in (D) ofFIG. 6 described above, in the communication by the pulse widthmodulation, a positive waveform and a negative waveform of the AC signal(in this case, the voltage V(L1) between the both ends of the powertransmission coil L1) are different from each other (are asymmetric),and contains so-called even harmonic component (containing second orderharmonic). In this example, when the AC signal is demodulated (envelopis detected) by the secondary-side unit, noise of the even harmoniccomponent distorts the communication waveform. Therefore, carrier tonoise ratio (C/N ratio) may be deteriorated, and communication qualitymay be lowered.

In contrast, in the communication by the amplitude modulation, forexample, as illustrated by a dashed line in (D) of FIG. 12, a positivewaveform and a negative waveform of the AC signal (the voltage V(L1)between the both ends of the power transmission coil L1) are coincidentwith each other (are symmetric), and contains so-called odd harmoniccomponent. Therefore, the C/N ratio in demodulation of the AC signal(envelope detection) by the secondary-side unit is improved, and thusthe communication quality is also improved.

As described above, in the present embodiment, the power limitingoperation by the power limiting modulation circuit 112A is controlledduring the communication period Tc to perform the communication by theamplitude modulation. Therefore, in addition to the effects of the firstembodiment, the communication quality during the communication period Tcis allowed to be improved. In addition, since the power limitingmodulation circuit 112A performs both the power limiting operation andthe modulation operation (the amplitude modulation operation) (has bothfunctions). Therefore, it is possible to achieve cost reduction of theunit, reduction in the number of mounted components, and size reduction.

(Modification)

As described above, although the technology of the present disclosurehas been described with reference to some embodiments, the presenttechnology is not limited to the embodiments, and various modificationsmay be made.

For example, in the above-described embodiments, various kinds of coils(the power transmission coil and the power reception coil) have beendescribed. However, various kinds of configurations are allowed to beused as the configurations (shapes) of the respective coils.Specifically, for example, each coil may be configured in shapes such asa spiral shape, a loop shape, a bar shape using a magnetic body, analpha-wound shape configured by folding a spiral coil into two layers, amultilayer spiral shape, a helical shape configured by winding a wire ina thickness direction thereof. Moreover, each coil is not limited to awinding coil configured of a conductive wire rod, and may be aconductive patterned coil configured of a printed board, a flexibleprinted board, or the like.

In addition, in the above-described embodiments, although the electronicapparatus has been described as an example of a unit to be fed withpower, the unit to be fed with power is not limited thereto, and may beother than the electronic apparatus (for example, vehicles such aselectric cars).

Furthermore, in the above-described embodiments, the components of eachof the feed unit and the electronic apparatuses have been specificallydescribed. However, all of the components are not necessarily provided,and other components may be further provided. For example, in the feedunit or the electronic apparatus, a communication function, a controlfunction, a display function, a function of authenticating asecondary-side unit, a function of determining whether a secondary-sideunit is placed on a primary-side unit, a function of detecting acontaminant such as a dissimilar metal, and the like may be provided.

In addition, in the above-described embodiments, mainly, the case wherethe feed system includes a plurality of (two) electronic apparatuses hasbeen described as an example. However, the number of electronicapparatuses is not limited thereto, and the feed system may include onlyone electronic apparatus.

Moreover, in the above-described embodiments, the charging tray for asmall electronic apparatus (CE device) such as a mobile phone has beendescribed as an example of the feed unit. However, the feed unit is notlimited to such a household charging tray, and is applicable as acharging unit for various electronic apparatuses, and the like. Inaddition, the feed unit is not necessarily a tray, and may be a standfor electronic apparatuses such as a so-called cradle.

(Example of Feed System Performing Non-Contact Power Transmission withUse of Electronic Field)

In addition, in the above-described embodiments, the case of the feedsystem that performs the non-contact power transmission (power feeding)from the feed unit as the primary-side unit to the electronic apparatusas the secondary-side unit with use of a magnetic field has beendescribed as an example. However, the configuration is not limitedthereto. Specifically, the contents of the present disclosure isapplicable to a feed system that performs non-contact power transmissionfrom a feed unit as a primary-side unit to an electronic apparatus as asecondary-side unit with use of an electronic field (electronic fieldcoupling), and similar effects to those in the above-describedembodiments may be obtained.

More specifically, for example, a feed system illustrated in FIG. 13 mayinclude one feed unit 81 (a primary-side unit) and one electronicapparatus 82 (a secondary-side unit). The feed unit 81 mainly has apower transmission section 810 including a power transmission electrodeE1 (a primary-side electrode), an AC signal source 811 (an oscillator),and a ground electrode Eg1. The electronic apparatus 82 mainly has apower reception section 820 including a power reception electrode E2 (asecondary-side electrode), a rectification circuit 821, a load 822, anda ground electrode Eg2. Specifically, the feed system includes two pairsof electrodes, the power transmission electrode E1 and the powerreception electrode E2, and the ground electrodes Eg1 and Eg2. In otherwords, each of the feed unit 81 (the primary-side unit) and theelectronic apparatus 82 (the secondary-side unit) has an antennaconfigured of a pair of asymmetric electrode structures, such as amonopole antenna therein.

In the feed system having such a configuration, when the powertransmission electrode E1 and the power reception electrode E2 face eachother, the above-described non-contact antennae are coupled with eachother (are coupled with each other by an electric field along a verticaldirection of the electrodes). Then, the induction field is generatedtherebetween, and power transmission using the electronic field isaccordingly performed (see power P8 illustrated in FIG. 13). Morespecifically, for example, as schematically illustrated in FIG. 14, thegenerated electric field (induction field Ei) propagates from the powertransmission electrode E1 side to the power reception electrode E2 side,as well as the generated induction field Ei propagates from the groundelectrode Eg2 side to the ground electrode Eg1 side. In other words, aloop path of the generated induction field Ei is formed between theprimary-side unit and the secondary-side unit. Also in such anon-contact power supply system using the electronic field, similareffects are allowed to be obtained by applying similar method to that inthe above-described embodiments.

Note that the present technology may be configured as follows.

(1) A feed unit including:

a power transmission section configured to perform power transmissionwith use of a magnetic field or an electric field;

a power limiting section provided on a power supply line from anexternal power source to the power transmission section; and

an operation stop section configured to forcibly stop the powertransmission, wherein

the operation stop section forcibly stops the power transmission when avoltage between an input and an output of the power limiting sectionexceeds a first threshold, and

the power limiting section forcibly interrupts power supply to the powertransmission section when the voltage between the input and the outputexceeds a second threshold, the second threshold being larger than thefirst threshold.

(2) The feed unit according to (1), wherein the operation stop sectionrenders a control signal for the power transmission invalid to forciblystop the power transmission.

(3) The feed unit according to (2), wherein the operation stop sectionincludes a switching section, the switching section being configured toswitch a state of the control signal between valid and invalid accordingto magnitude of the voltage between the input and the output.

(4) The feed unit according to any one of (1) to (3), wherein the powerlimiting section includes an error amplifier that is configured tocontrol power limiting operation based on a potential difference betweena reference voltage and a voltage corresponding to an input current fromthe external power source, and when the voltage between the input andthe output exceeds the second threshold, the power limiting sectioncontrols magnitude of the reference voltage to forcibly interrupt thepower supply to the power transmission section.

(5) The feed unit according to (4), wherein the power limiting sectionincludes a transistor on the power supply line, and controls themagnitude of the reference voltage and sets the transistor to OFF stateto forcibly interrupt the power supply to the power transmissionsection.

(6) The feed unit according to any one of (1) to (5), wherein

the first threshold defines whether the state of the unit is in anoverload state during normal operation, and

the second threshold defines whether the power transmission section isin a failed state or in a destructive state.

(7) The feed unit according to any one of (1) to (6), wherein theoperation stop section is in an inoperable state when the voltagebetween the input and the output exceeds the second threshold.

(8) The feed unit according to any one of (1) to (7), further including

a control section that includes a power transmission control section,the power transmission control section being configured to performcontrol of the power transmission.

(9) The feed unit according to (8), wherein the control section isprovided on a side closer to the external power source than the powerlimiting section.

(10) The feed unit according to (8) or (9), wherein the powertransmission control section controls the power transmission to allow afeeding period during which the power transmission is performed on aunit to be fed with power and a communication period during whichpredetermined communication is performed with the unit to be fed withpower, to be set in a time-divisional manner, and controls the powerlimiting operation by the power limiting section to allow communicationby amplitude modulation to be performed during the communication period.

(11) The feed unit according to (10), wherein the power limiting sectionperforms the power limiting operation during the feeding period, andperforms amplitude modification operation during the communicationperiod.

(12) The feed unit according to any one of (8) to (11), wherein

the power transmission control section controls the power transmissionto allow a feeding period during which the power transmission isperformed on a unit to be fed with power and a communication periodduring which predetermined communication is performed with the unit tobe fed with power, to be set in a time-divisional manner, and

the operation stop section forcibly stops the communication when thevoltage between the input and the output exceeds the first thresholdduring the communication period.

(13) The feed unit according to any one of (8) to (12), furtherincluding

an AC signal generation section configured to generate an AC signal toperform the power transmission, wherein

the power transmission control section controls operation of the ACsignal generation section to perform control of the power transmission.

(14) The feed unit according to (13), wherein

the AC signal generation section is configured using a switchingamplifier including a switching device, and

the power transmission control section uses a control signal for thepower transmission to control ON-OFF operation of the switching device.

(15) The feed unit according to (14), wherein the power transmissioncontrol section controls the power transmission to allow a feedingperiod during which the power transmission is performed on a unit to befed with power and a communication period during which predeterminedcommunication is performed with the unit to be fed with power, to be setin a time-divisional manner, and controls a duty ratio of the controlsignal to allow communication by pulse width modulation to be performedduring the communication period.

(16) The feed unit according to any one of (8) to (15), wherein thecontrol section includes the power transmission control section and acontrol section for data transmission.

(17) The feed unit according to any one of (1) to (16), wherein thepower transmission section uses resonance operation to perform the powertransmission.

(18) The feed unit according to any one of (1) to (17), wherein theoperation stop section includes a voltage detection section that isconfigured to detect the voltage between the input and the output.

(19) A feed system provided with one or a plurality of electronicapparatuses and a feed unit configured to perform power transmission onthe electronic apparatuses, the feed unit including:

a power transmission section configured to perform the powertransmission with use of a magnetic field or an electronic field;

a power limiting section provided on a power supply line from anexternal power source to the power transmission section; and

an operation stop section configured to forcibly stop the powertransmission, wherein

the operation stop section forcibly stops the power transmission when avoltage between an input and an output of the power limiting sectionexceeds a first threshold, and

the power limiting section forcibly interrupts power supply to the powertransmission section when the voltage between the input and the outputexceeds a second threshold, the second threshold being larger than thefirst threshold.

This application is based upon and claims the benefit of priority of theJapanese Patent Application No. 2011-231766 filed on Oct. 21, 2011, andthe Japanese Patent Application No. 2012-92848 filed on Apr. 16, 2012,both filed with the Japan Patent Office, the entire contents of theseapplications are incorporated herein by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A feed unit comprising: a power transmission section configured toperform power transmission with use of a magnetic field or an electricfield; a power limiting section provided on a power supply line from anexternal power source to the power transmission section; and anoperation stop section configured to forcibly stop the powertransmission, wherein the operation stop section forcibly stops thepower transmission when a voltage between an input and an output of thepower limiting section exceeds a first threshold, and the power limitingsection forcibly interrupts power supply to the power transmissionsection when the voltage between the input and the output exceeds asecond threshold, the second threshold being larger than the firstthreshold.
 2. The feed unit according to claim 1, wherein the operationstop section renders a control signal for the power transmission invalidto forcibly stop the power transmission.
 3. The feed unit according toclaim 2, wherein the operation stop section includes a switchingsection, the switching section being configured to switch a state of thecontrol signal between valid and invalid according to magnitude of thevoltage between the input and the output.
 4. The feed unit according toclaim 1, wherein the power limiting section includes an error amplifierthat is configured to control power limiting operation based on apotential difference between a reference voltage and a voltagecorresponding to an input current from the external power source, andwhen the voltage between the input and the output exceeds the secondthreshold, the power limiting section controls magnitude of thereference voltage to forcibly interrupt the power supply to the powertransmission section.
 5. The feed unit according to claim 4, wherein thepower limiting section includes a transistor on the power supply line,and controls the magnitude of the reference voltage and sets thetransistor to OFF state to forcibly interrupt the power supply to thepower transmission section.
 6. The feed unit according to claim 1,wherein the first threshold defines whether the state of the unit is inan overload state during normal operation, and the second thresholddefines whether the power transmission section is in a failed state orin a destructive state.
 7. The feed unit according to claim 1, whereinthe operation stop section is in an inoperable state when the voltagebetween the input and the output exceeds the second threshold.
 8. Thefeed unit according to claim 1, further comprising a control sectionthat includes a power transmission control section, the powertransmission control section being configured to perform control of thepower transmission.
 9. The feed unit according to claim 8, wherein thecontrol section is provided on a side closer to the external powersource than the power limiting section.
 10. The feed unit according toclaim 8, wherein the power transmission control section controls thepower transmission to allow a feeding period during which the powertransmission is performed on a unit to be fed with power and acommunication period during which predetermined communication isperformed with the unit to be fed with power, to be set in atime-divisional manner, and controls the power limiting operation by thepower limiting section to allow communication by amplitude modulation tobe performed during the communication period.
 11. The feed unitaccording to claim 10, wherein the power limiting section performs thepower limiting operation during the feeding period, and performsamplitude modification operation during the communication period. 12.The feed unit according to claim 8, wherein the power transmissioncontrol section controls the power transmission to allow a feedingperiod during which the power transmission is performed on a unit to befed with power and a communication period during which predeterminedcommunication is performed with the unit to be fed with power, to be setin a time-divisional manner, and the operation stop section forciblystops the communication when the voltage between the input and theoutput exceeds the first threshold during the communication period. 13.The feed unit according to claim 8, further comprising an AC signalgeneration section configured to generate an AC signal to perform thepower transmission, wherein the power transmission control sectioncontrols operation of the AC signal generation section to performcontrol of the power transmission.
 14. The feed unit according to claim13, wherein the AC signal generation section is configured using aswitching amplifier including a switching device, and the powertransmission control section uses a control signal for the powertransmission to control ON-OFF operation of the switching device. 15.The feed unit according to claim 14, wherein the power transmissioncontrol section controls the power transmission to allow a feedingperiod during which the power transmission is performed on a unit to befed with power and a communication period during which predeterminedcommunication is performed with the unit to be fed with power, to be setin a time-divisional manner, and controls a duty ratio of the controlsignal to allow communication by pulse width modulation to be performedduring the communication period.
 16. The feed unit according to claim 8,wherein the control section includes the power transmission controlsection and a control section for data transmission.
 17. The feed unitaccording to claim 1, wherein the power transmission section usesresonance operation to perform the power transmission.
 18. The feed unitaccording to claim 1, wherein the operation stop section includes avoltage detection section that is configured to detect the voltagebetween the input and the output.
 19. A feed system provided with one ora plurality of electronic apparatuses and a feed unit configured toperform power transmission on the electronic apparatuses, the feed unitcomprising: a power transmission section configured to perform the powertransmission with use of a magnetic field or an electronic field; apower limiting section provided on a power supply line from an externalpower source to the power transmission section; and an operation stopsection configured to forcibly stop the power transmission, wherein theoperation stop section forcibly stops the power transmission when avoltage between an input and an output of the power limiting sectionexceeds a first threshold, and the power limiting section forciblyinterrupts power supply to the power transmission section when thevoltage between the input and the output exceeds a second threshold, thesecond threshold being larger than the first threshold.